Collaborative sensor coordination among the systems of a system of systems (SOS) is currently being pursued by the Missile Defense Agency (MDA) to enhance both targeting and cueing accuracies in support of ballistic missile defense. Collaborative sensor coordination requires each element of Ballistic Missile Defense System (BMDS) to register its sensor(s) to local geodetic coordinate systems in order to minimize tracking and guidance errors, thereby reducing system handover and guidance errors between the target tracking and/or cueing systems and the interceptor(s). Ultimately this “sensor registration” provides additional margin to the weapon system's pointing and divert error budgets.
Sensor registration involves mitigation of the effects of both angular and positional bias errors associated with each sensor. Angular sensor bias registration has been addressed through state augmentation in U.S. patent application Ser. No. 11/149,692, filed Jun. 10, 2005 in the name of Boka et al. and entitled “Instantaneous Multisensor Angular Bias Autoregistration” (ISAAC), and “System Calibration using Satellites (SCUS)” represented by U.S. Pat. No. 5,729,234, entitled “Remote alignment system” issued Mar. 17, 1998 in the name of Stetson et al. This system assumes that positional sensor bias registration error is not present. However, such sensor position bias registration error can exist.
FIG. 1 illustrates a scenario 10 in which a ship-borne radar system 12 lies at a radius R from the earth's center. A vector X represents a line-of-sight from the ship's radar to a target missile 14, which may be ballistic, on a true ballistic trajectory 16. A vector Z represents a position vector from the center of the earth to the target 14, and ω represents the earth rate vector. The vector δX represents the unknown sensor position bias. As a result of the bias, the measured or biased-position trajectory 18 deviates from the true position trajectory 16. The true ballistic trajectory 16 of target missile 14 extends to a land mass 21.
Current technology in positional sensor bias registration relies on the Global Positioning System (GPS) to provide an absolute positional reference that is estimated using a GPS receiver coupled with an embedded extended Kalman filter. GPS receivers are, however, susceptible to jamming and spoofing failure modes, which can ultimately corrupt the absolute positional reference estimate. These modes of GPS failures are highly probable in some wartime environments, and alternative methods for positional sensor bias registration are desired.